The present invention is in the field of optical amplifiers. More specifically, the present invention is intended to be an alternative for erbium doped fiber amplifiers (xe2x80x9cEDFAxe2x80x9d) and used in applications similar to EDFAs.
Optical amplifiers are commonly used in optical networks and, in fact, required for most optical networks. Optical networks use silica-based fibers for transmission of optical signals. Optical networks carry multiple signals from point to point simultaneously through the use of different channels, wherein each channel represents a distinct wavelength. The limit on the number of signal transmitted through the fiber is limited by the number of available channels. The number of available channels is limited by many factors, including how closely spaced can the channels be before neighboring channels overlap and interfere with each other. Another concern, from a temporal standpoint, is how frequently can digital signals be generated and accurately detected at any given time.
These limitations can be alleviated by making use of previously unavailable wavebands (bands of wavelengths). The C-band is the center of the optical transmission window and is typically the only band efficiently used in optical networks. Ideally, an optical network would make use of the S-band, conventionally described as 1.48 to 1.52 microns, and the L-band, conventionally described as 1.57 to 1.605 microns, which appear on either side of the C-band. EDFAs do not operate in the S-band and are very inefficient in the L-band.
EDFAs exhibit peak gain coefficients between 1.53 and 1.57 microns of between 1 dB/m and 1.5 dB/m. In the L-band, which is over 1.57 microns, gain coefficients for EDFAs are 5 times below the peak, experienced in the C-band. To compensate for the reduced gain coefficient in the longer waveband, the length of the fiber must be increased five-fold. The longer fiber length in the L-band for EDFAs introduces more passive fiber loss and decreases overall conversion efficiency. The loss can only be overcome by increasing the diode pump power.
The present invention is the result of the realization that Erbium doped crystals can provide amplification over a broader wavelength range, more efficiently than Erbium doped fiber. More specifically, Erbium doped crystal amplifiers are far more efficient for amplifying signals in the L-band than EDFAs.
Therefore, an object of this invention is to efficiently amplify optic signals in the L-band.